It has often been remarked that the simple shepherds who inhabit literary Arcadia are impressively – suspiciously – well-read. But not until last weekend had those bookish shepherds ever been given their own literary festival.

The Arcadia in question was not from a poem but tangible: the superb Capability Brown landscape of Petworth House in Sussex. And the Arcadians assembled were not exactly shepherds but that other literate sort of plein airist (equally at home among books and trees): gardeners.

The Garden Museum's Festival of Garden Literaturecomprised two days of talks addressing the connection between gardens and a wider culture. The variety was wide: Robin Lane Fox, for instance, spoke on the early Christians and their shifting moral stance on gardens; art historian Andrew Wilton on gardens and Turner; the nature writer Richard Mabey on the history of walled gardens.

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The entire festival (a very intimate affair) was tucked away in Lord and Lady Egremont's serene and private garden on Petworth's south flank. They held very discreet court: Lady Egremont spoke on the walled flower garden, her creation, while the acclaimed historian Lord Egremont led a complex discussion of First World War poets and their fictive, "golden" pre-war England.

A pre-war England romanticised, of course: the crumbling labourers' cottages those poets so eagerly snapped up, then later dreamt of, were crumbling precisely because England wasn't golden – rural poverty was desperate. Interestingly, the poets' response to the landscape of their battlefields was similarly emotional: the chalk-downs of France seemed to them like Wiltshire without the stockbrokers. "They particularly appreciated the Somme," said Lord Egremont, hastily adding: "Not the battle, of course."

An extract from Siegfried Sassoon's memoir ("beautiful prose, but sedative," remarked Egremont) underlined the melancholy of that poet's career: he never truly "escaped" the Great War, where he found his voice, and would dwell on it nostalgically through memoir right into the Forties and Fifties.

If Siegfried Sassoon eked out his days looking backward, the same could not be said of early Christians and their gardens. Robin Lane Fox demonstrated how the first Christians' distaste for gardens as a symbol of pagan luxury and leisure was swiftly overcome until, by the Middle Ages, monastic communities undertook vast gardens whilst horticultural figures of thought ("Christ as gardener"; "the Virgin Mary as hortus conclusus") became the norm. Lane Fox, despite complaining that recent bacchanals had left his wits in a state of numbness, proved more than amply on-the-ball, cropping up to participate in discussions all day long.

Anna Pavord, journalist and author, considered how novelists have used gardens to delineate character: from the leisurely Lord Emsworth in PG Wodehouse's Blandings ("That evening, he planned to read a pig book in the library, take a sniff at a rose or two and possibly do a bit of snailing") to the claws-out rosebed rivalries in Mapp and Lucia, EF Benson's satire on interwar provincial life.

Conversely, the biographer Victoria Glendinning (whose landmark 1983 portrait of Vita Sackville-West traced subtleties in her character by examining the development of Sissinghurst) asked what we can learn of a historical person from their garden.

One of most charming things about the Festival of Garden Literature was the absence of any thick-set barrier between speaker and audience: the occasional good-natured heckle from old friends and colleagues turned each talk into a conversation; lunch, meanwhile, was a communal, egalitarian affair (crisp young asparagus, salad and strawberries). It was a tiny, coherent, exquisite party for those who find gardening contemplative – an art form, but also a cultural force – and wanted to think on it more.

This was Hay Festival for those who know exactly what they want – the theme ('A Friend, A Book, A Garden', taken from one of John Evelyn's letters) was focused but not at all constricting. This was Hay, too, on a more than manageable scale: 100 people in two tiny pavilions of white linen with hand-turned wooden finials and a sweet little cosmos of gold-braid stars on the interior ceiling. In opera terms, it was the serenity of the Grange after the hurly-burly of Glyndebourne and the glitz of rehoused Garsington.

Next year, the Festival of Garden Literature will not be at Petworth again; this nimble event moves every year to a different garden (last year it was hosted by the garden designer Tom Stuart-Smith). But wherever this blissful young festival roams in future, it's certainly worth downing tools to follow it.